'94 940 NA. Since the temps began to drop, the car has idled very rough for about 30 seconds after cold start and then normal running. There is pungent white smoke out the tail. This didn't happen during the holiday week in Florida. Warm start, no problem and no white smoke. I'm thinking coolant temp sensor. Luckily I have a parts car standing by. Any directionn would be appreciated.
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89 240 Wagon 217K, 94 940 185K

I don't know if this helps, but I fought the same problem for the last 3 winters. The car was hard to start when the temperature reached freezing and required extensive cranking. Once it started, it ran fine. Without going into all the painful things I attempted to correct the problem, I finally found that it was a damaged spark plug where the gap had significantly increased. You may want to pull yours to see if this is the case. It was a $1.60 fix for a problem I had spent hundreds of dollars trying correct and expended a lot of heartache.

hi j.pelchat,
I'm going through similar problems in the UK, (below zero at moment). Have cleaned out the IAC controller a couple of times, (seems to suffer a bit from occasional sticking) but still have an intermittent rough idle, more like a misfire when it ticks over after a couple of minutes).

Q. I see you're starting with temp control sensor, do you have a reading on the dash instrument?

regards
pierso

the problem occurs only at startup with a cold engine. The instrument on the dash is the coolant temp gauge and it doesn't have a chance to move before the idle corrects itself. Haven't had a chance to work on the problem yet

Yep, start with the CTS.
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84 242Ti IPD bars&springs, 89 745 16v M46 IPD bars, 89 744 16v M46 IPD bars, 93 945 Turbo AW71, 91 245SE AW70 IPD bars, 93 245 CLassic M47